In mobile communication systems, a mobile communication unit, commonly referred to as a mobile device, must be capable of detecting channels which are available for communication with one or more base stations (BSs). For example, although a particular communications system may carry several different communications channels, all of the communications channels may not always be available to the mobile device or available in the geographical area in which the mobile device is situated. Consequently, if the mobile device is powered off and then on again, or moves from a service area of one of the BSs to the service area of another BS, the mobile device must execute a channel scanning routine to identify the communication channels available to the mobile device. Two channel scanning routines are commonly used to identify available communications channels.
According to one channel scanning routine, the mobile device measures the average signal power of all channels within the frequency band in which the mobile device is designed to operate, and then selects a communication channel whose measured power exceeds a predetermined threshold power rating. According to another channel scanning routine, the mobile device performs a power spectral measurement of all channels within the frequency band in which the mobile device is designed to operate, and then selects a communication channel in accordance with the spectral measurements. However, these techniques have a number of deficiencies.
Most significantly, the conventional channel scanning routines are prone to false positives, namely incorrectly identifying unavailable channels as possible available channels. Further channel qualification functions such as monitoring a channel for a synchronization pattern or signal are then normally performed for channels identified as possible available channels. These further qualification functions can be time intensive and as such, false positives cause a mobile device to waste computing and power resources performing such functions for unavailable channels.
Attempts have been made to address the time required to detect an available communications channel. In accordance with one such approach, instead of the mobile device always scanning each channel within the frequency band in which the mobile device is designed to operate, the mobile device maintains a list of the most recently-used communications channels, and initially scans only the most recently-used communication channels as identified on the list. If none of the most recently-used channels are available, the mobile device then scans the remaining communications channels. Although this latter approach can reduce the channel detection time, it is still prone to indicating false positives.
Therefore, there remains a need for a communications channel detector and channel detection method which reduces the number of false positives.
There remains a related need for a communications channel detector and channel detection method which determines the availability of a desired type of communications channel in a communication system.